The present invention relates to a multi-cylinder internal combustion engine with externally applied ignition that is supercharged by means of a turbocharger whereby the charging air is cooled in a charging air cooler prior to entry into the cylinder head of the internal combustion engine and whereby an ignition distributor is provided whose distributor housing surrounding the same is forcibly traversed by air flow.
Sparks occur in the ignition distributor of an internal combustion engine during the interruption of the high voltage current which lead to the formation of ozone and nitrogen oxide. The ozone has a strong oxidation effect and in case of protracted interaction causes corrosions at the electrical contacts and other metal parts of the ignition distributor. Also, the aging of the lubricating grease at the bearing places of the ignition distributor is accelerated by the ozone interaction in an undesired manner. One therefore aims to remove the thus-forming ozone as rapidly as possible out of the housing of the ignition distributor. According to the DE-OS No. 33 22 545, this takes place in that a blade rotor is secured on the distributor shaft, which discharges gases out of the ignition distributor through openings in the distributor housing into the atmosphere. Whereas at normal atmospheric pressure at sea level, this protective measure suffices, an increased danger of spark discharge or arcing exists at greater geodetic heights by reason of the smaller pressure of the atmospheric and the smaller air density in the distributor housing and therewith an increased danger of misfirings in the internal combustion engine.
It is therefore the object of the present invention to enable a still more effective air through-flow of the ignition distributor in an internal combustion engine with externally applied ignition and supercharged by means of a turbocharger which is particularly well-suited as drive aggregate for aircrafts at greater heights.
If, as solution to the underlying problem, the charging air line leading from the turbocharger to the cylinder head is connected to the distributor housing of the ignition distributor, then the inlet pressure to the distributor housing lies already at sea level above the atmospheric pressure. This pressure difference takes care that a good through-flow of the ignition distributor is assured.
In order to avoid a loss in charging air, in an advantageous construction according to the present invention, the distributor housing is so arranged in a by-pass line to the charging air cooler that the charging air branched off upstream of the charging air cooler again terminates in the charging air line downstream of the charging air cooler after flowing through the distributor housing. The pressure difference resulting at the charging air cooler is available for the through-flow. If the charging pressure is kept constant independently of the geodetic height in order to assure a constant power output of the internal combustion engine at all flight elevations, also the air density in the distributor housing has a constant value; spark discharges from the one to the other contact place can be avoided in this manner.